Dielectric resonator antennas are resonant antenna devices that radiate or receive radio waves at a chosen frequency of transmission and reception, as used in for example in mobile telecommunications. In general, a DRA consists of a volume of a dielectric material (the dielectric resonator) disposed on or close to a grounded substrate, with energy being transferred to and from the dielectric material by way of monopole probes inserted into the dielectric material or by way of monopole aperture feeds provided in the grounded substrate (an aperture feed is a discontinuity, generally rectangular in shape, although oval, oblong, trapezoidal or butterfly/bow tie shapes and combinations of these shapes may also be appropriate, provided in the grounded substrate where this is covered by the dielectric material. The aperture feed may be excited by a strip feed in the form of a microstrip transmission line, coplanar waveguide, slotline or the like which is located on a side of the grounded substrate remote from the dielectric material). Direct connection to and excitation by a microstrip transmission line is also possible. Alternatively, dipole probes may be inserted into the dielectric material, in which case a grounded substrate is not required. By providing multiple feeds and exciting these sequentially or in various combinations, a continuously or incrementally steerable beam or beams may be formed, as discussed for example in the present applicant's co-pending U.S. patent application Ser. No. 09/431,548 and the publication by KINGSLEY, S. P. and O'KEEFE, S. G., “Beam steering and monopulse processing of probe-fed dielectric resonator antennas”, IEE Proceedings—Radar Sonar and Navigation, 146, 3, 121-125, 1999, the full contents of which are hereby incorporated into the present application by reference.
The resonant characteristics of a DRA depend, inter alia, upon the shape and size of the volume of dielectric material and also on the shape, size and position of the feeds thereto. It is to be appreciated that in a DRA, it is the dielectric material that resonates when excited by the feed. This is to be contrasted with a dielectrically loaded antenna (DLA), in which a traditional conductive radiating element is encased in a dielectric material that modifies the resonance characteristics of the radiating element. As a further distinction, a DLA has either no, or only a small, displacement current flowing in the dielectric whereas a DRA or HDA has a non-trivial displacement current.
Dielectric resonators may take various forms, a common form having a cylindrical shape or half- or quarter-split cylindrical shape. The resonator medium can be made from several candidate materials including ceramic dielectrics.
Since the first systematic study of dielectric resonator antennas (DRAs) in 1983 [LONG, S. A., McALLISTER, M. W., and SHEN, L. C.: “The Resonant Cylindrical Dielectric Cavity Antenna”, IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406-412], interest has grown in their radiation patterns because of their high radiation efficiency, good match to most commonly used transmission lines and small physical size [MONGIA, R. K. and BHARTIA, P.: “Dielectric Resonator Antennas—A Review and General Design Relations for Resonant Frequency and Bandwidth”, International Journal of Microwave and Millimetre-Wave Computer-Aided Engineering, 1994, 4, (3), pp 230-247]. A summary of some more recent developments can be found in PETOSA, A., ITTIPIBOON, A., ANTAR, Y. M. M., ROSCOE, D., and CUHACI M.: “Recent advances in Dielectric-Resonator Antenna Technology”, IEEE Antennas and Propagation Magazine, 1998, 40, (3), pp 35-48.
A variety of basic shapes have been found to act as good dielectric resonator structures when mounted on or close to a ground plane (grounded substrate) and excited by an appropriate method. Perhaps the best known of these geometries are:    Rectangle [McALLISTER, M. W., LONG, S. A. and CONWAY G. L.: “Rectangular Dielectric Resonator Antenna”, Electronics Letters, 1983, 19, (6), pp 218-219].    Triangle [ITTIPIBOON, A., MONGIA, R. K. ANTAR, Y. M. M., BHARTIA, P. and CUHACI, M.: “Aperture Fed Rectangular and Triangular Dielectric Resonators for use as Magnetic Dipole Antennas”, Electronics Letters, 1993, 29, (23), pp 2001-2002].    Hemisphere [LEUNG, K. W.: “Simple results for conformal-strip excited hemispherical dielectric resonator antenna”, Electronics Letters, 2000, 36, (11)]    Cylinder [LONG, S. A., McALLISTER, M. W., and SHEN, L. C.: “The Resonant Cylindrical Dielectric Cavity Antenna”, IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406-412].    Half-split cylinder (half a cylinder mounted vertically on a ground plane) [MONGIA, R. K., ITTIPIBOON, A., ANTAR, Y. M. M., BHARTIA, P. and CUHACI, M: “A Half-Split Cylindrical Dielectric Resonator Antenna Using Slot-Coupling”, IEEE Microwave and guided Wave Letters, 1993, Vol. 3, No. 2, pp 38-39].
Some of these antenna designs have also been divided into sectors. For example, a cylindrical DRA can be halved [TAM, M. T. K. and MURCH, R. D.: “Half volume dielectric resonator antenna designs”, Electronics Letters, 1997, 33, (23), pp 1914-1916]. However, dividing an antenna in half, or sectoring it further, does not change the basic geometry from cylindrical, rectangular, etc.
High dielectric antennas (HDAs) are similar to DRAS, but instead of having a full ground plane located under the dielectric resonator, HDAs have a smaller ground plane or no ground plane at all. DRAs generally have a deep, well-defined resonant frequency, whereas HDAs tend to have a less well-defined response, but operate over a wider range of frequencies.
In both DRAs and HDAs, the primary radiator is the dielectric resonator. In DLAs the primary radiator is a conductive component (e.g. a copper wire or the like) and the dielectric modifies the medium in which the antenna operates, and generally makes the antenna smaller. A simple way to make a printed monopole antenna is to extend a microstrip into a region where there is no grounded substrate on the other side of the board.
It is known that one dielectric resonator antenna can excite another one parasitically. Indeed, the effects of parasitic dielectric resonator antennas on a cylindrical dielectric resonator antenna were studied as early as 1993 [Simons, R.; Lee, R.; “Effect of parasitic dielectric resonators on CPW/aperture-coupled dielectric resonator antennas”, IEE proceedings-H, 140, pp. 336-338, 1993]. A similar study for a parasitic three-element array of rectangular dielectric resonator antennas was reported in 1996 [Fan, Z.; Antar, Y.; Ittipiboon, A.; Petosa, A.; W “Parasitic coplanar three element dielectric resonator antenna subarray”, Electronics Letters, 32, pp. 789-790, 1996].
It is also known that a dielectric resonator antenna with one probe feed can have another feed excited parasitically, i.e. the second feed is not driven by the electronic circuitry [Long, R.; Dorris, R.; Long, S.; Khayat, M.; Williams, J.; “Use of Parasitic Strip to produce circular polarisation and increased Bandwidth for cylindrical Dielectric Resonator Antenna”, Electronics Letters, 37, pp. 406-408, 2001].
Proc. Natl. Sci. Counc. ROC(A), Vol 23, No 6, 1999, pp 736-738, C.-S. Hong, “Adjustable frequency dielectric resonator antenna” discloses a DRA directly fed by a microstrip transmission line, and further provided with a conductive parasitic disc element adjustably mounted over a top surface of the DRA. The disc element is moved closer to or further away from the top surface of the DRA so as to tune the DRA to predetermined frequencies. It is to be noted that the parasitic disc element is not configured so as to act as a useful radiating antenna component in its own right, but merely to tune the DRA.
EEE Transactions on Vehicular Technology, Vol 48, No 4, July 1999, pp 1029-1032, Z. N. Chen et al., “A new inverted F antenna with a ring dielectric resonator” discloses a wire IFA (WIFA) with a first, driven leg, a second, parasitic leg and a third, horizontal element connected to both legs. The horizontal element is formed as a probe in dielectric disc, causing the disc to act as a DRA. The conducting antenna component (the WIFA) is driven, with one part of the WIFA in turn driving a DRA. Although the WIFA has a parasitic leg, this is not parasitically driven by the DRA per se.
EP 1 271 691 (Filtronic) discloses a DRA having a direct feedline 231 that, in addition to driving the DRA, serves itself as a radiator in the same frequency range as the DRA. FIG. 2 shows one embodiment in which the dielectric pellet 220 rests on a groundplane 210, and in which two sides 221, 222 of the pellet are metallised. The feedline 231 contacts the top surface 223 of the pellet 220 and thus drives the pellet 220, while also being configured to radiate in the same frequency range as the pellet 220. The DRA does not parasitically drive any further antenna components. An alternative embodiment is shown in FIGS. 5a and 5b, where a direct feedline 531 is disposed between the bottom of the pellet 520 and the groundplane 510. An additional parasitic element 532 is disposed under the pellet, but this is not parasitically driven by the DRA, but merely serves to broadband the direct feedline 531. In other words, the parasitic element 532 is excited by the direct feedline 531 and not by the DRA.
WO 03/019718 (CNRS et al.) discloses a stripline-fed DRA mounted on a groundplane, with a “parasitic element” 50 located on top of the pellet so as to create an asymmetry. The parasitic element 50 is not in itself configured or designed to radiate in a useful manner.
Electronic Letters, Vol 37, No 7, March 2001, pp 406-408, R. T. Long et al., “Use of a parasitic strip to produce circular polarisation and increased bandwidth for cylindrical dielectric resonator antennas” discloses an arrangement in which one or more parasitic strips are provided on side surfaces of a cylindrical DRA so as to improve bandwidth and to produce circular polarisation. Again, the parasitic strips are configured solely to modify resonant characteristics of the DRA, and are not designed to radiate themselves in a useful manner.
There appear to be no reports in the literature, however, of dielectric antennas being used to excite conventional antennas such as patches, PILAs (planar inverted-L antennas), dipoles, slot antennas, etc. in such a way that both the dielectric antenna and the conventional parasitic antenna radiate at useful frequencies and in a manner that is mutually compatible, for example with a view to providing a hybrid antenna with broadband or multiband operation.